Gamma-ray Astrophysics and Motivation: Gamma-ray astrophysics is an exciting field of high-energy particle physics that has expanded dramatically in the past decade. The science of gamma-ray cosmology presents a way of looking at the most interesting parts of the universe. Very high energetic particles in space indicate the existence of exotic and extreme physical conditions. Looking for gamma- ray emissions allows us to map the universe, discovering high magnetic/electric fields, shock waves, and cataclysmic explosions. These emissions offer the only direct probe of the extreme conditions in these exciting phenomena .
Very energetic particles are extremely difficult to detect. Charged particles are affected by the incredibly strong magnetic fields of deep space, so when they reach earth it is impossible to deduce the origins of the particle. Gamma rays are unaffected by these magnetic fields. A gamma ray is a packet of electromagnetic energy photons. They are the most energetic photons in the electromagnetic spectrum, and they are emitted from the nuclei of unstable radioactive atoms. They travel in straight lines allowing astronomical instruments to determine the origins of the high-energy particles. However, there is an inverse relationship between particle energy and particle flux; higher energies result in very little flux. Space-based instruments are expensive and too small to properly detect higher energy particles. Modern projects use ground-based instruments designed specifically to detect gamma rays. It does so through secondary radiation detection. The process is visualized in figure 1: A source emits a gamma ray. The gamma ray interacts with the nitrogen in the atmosphere, producing a shower of electrons, positrons, and other particles as the gamma ray decays. This particle shower is seen as a radiation called “Cherenkov light.” Large optical reflectors in the ground-based telescope then image the Cherenkov light onto a photomultiplier tube camera in the instrument. Multiple telescopes imaging the same Cherenkov radiation allow us to triangulate and pinpoint the origin of the particle shower with a 3D reconstruction of the shower in the sky .